The proteins encoded in the Major Histocompatibility Complex region of the genome are involved in many aspects of immunological recognition. It is known that all mammals and probably all vertebrates possess basically equivalent MHC systems and that immune response genes are linked to the MHC.
In man the major histocompatibility complex is the HLA gene cluster on chromosome 6. The main regions are D, B, C, and A. The D region contains genes for Class II proteins which are involved in cooperation and interaction between cells of the immune system. Many diseases have been found to be associated with the D region of the HLA gene cluster. Studies to date have shown associations with an enormous variety of diseases including most autoimmune diseases (see for example European Patent No. 68790). European Patent No. 68790 suggests controlling diseases associated with a particular allele of certain regions of the MHC such as the HLA-D region in humans by selectively suppressing the immune response(s) controlled by a monoclonal antibody specific for an MHC-Class II antigen.
L243 is a murine IgG2A anti-HLA DR antibody which we believe to be of particular use in treatment of diseases such as autoimmune diseases since it shows particularly potent suppression of in vitro immune function and is monomorphic for all HLA-DR.
Since most available monoclonal antibodies are of rodent origin, they are naturally antigenic in humans and thus can give rise to an undesirable immune response termed the HAMA (Human Anti-Mouse Antibody) response. Therefore, the use of rodent monoclonal antibodies as therapeutic agents in humans is inherently limited by the fact that the human subject will mount an immunological response to the antibody and will either remove it entirely or at least reduce its effectiveness.
Proposals have been made for making non-human MAbs less antigenic in humans. Such techniques can be generically termed `humanisation` techniques. These techniques generally involve the use of recombinant DNA technology to manipulate DNA sequences encoding the polypeptide chains of the antibody molecule. A simple form of humanisation involves the replacement of the constant regions of the murine antibody with those from a human antibody [Morrison et al (1984) Proc. Natl. Acad. Sci. USA 81 6851-55; Whittle et al (1987) Prot. Eng. 1 499-505]. The lowering of the level of the HAMA response to the chimeric antibodies leads to the expectation that further humanisation of the variable region outside of the antigen binding site may abolish the response to these regions and further reduce any adverse response.
A more complex form of humanisation of an antibody involves the redesign of the variable region domain so that the amino acids constituting the murine antibody binding site are integrated into the framework of a human antibody variable region. Humanisation has led to the reconstitution of full antigen binding activity in a number of cases [Co et al (1990) J. Immunol. 148 1149-1154; Co et al (1992) Proc. Natl. Acad. Sci. USA 88 2869-2873; Carter et al (1992) Proc. Natl. Acad. Sci. 89 4285-4289; Routledge et al (1991) Eur. J. Immunol. 21 2717-2725 and International Patent Specifications Nos. WO 91/09967; WO 91/09968 and WO 92/113831.
It can therefore be anticipated that the humanisation of L243 may lead to reduced immunogenicity in man and overcome the potential problem of the HAMA response previously associated with the use of murine antibodies in humans.
We have now prepared recombinant antibody molecules having specificity for the epitope recognised by the murine monoclonal antibody L243.